Tumor hypoxia, observed in all types of human tumors, is an independent prognosticator of malignant progression and poor patient survival. The conventional wisdom is that hypoxic tumor cells are resistant to conventional therapy and is highly metastatic. Therefore, targeting hypoxic tumor cells has inevitably become a focus of current cancer treatment plans as well as drug development efforts. Unfortunately, there remains a lack of definitive answers about the true malignant phenotypes and characteristics of hypoxic tumor cells in vivo, which partly explains the lack of convincing benefits of targeting hypoxic tumor cells in clinical trials so far. To addrss these pertinent questions, we propose an innovative approach to specifically mark hypoxic cells for in vivo identification or ex vivo isolation, as well as to follow their metastatic journey and o monitor cell fate after anti-cancer treatment in vivo. We will also use this innovative strategy to conduct targeted investigation of signaling pathways specifically in hypoxic cells in vivo without the unwanted interference from the adjacent non-hypoxic tumor cells.